Right, and you can land on the moon with basic newtonian mechanics. The are millions of devils in the details but for a person to decide how big a rocket to bui

Right, and you can land on the moon with basic newtonian mechanics. The are millions of devils in the details but for a person to decide how big a rocket to build and whether it could land vertically after a payload of X that needs a delta-V of Y, its easy napkin math to prove feasibility. Executing it is then one of the hardest things people can do but SpaceX had all the best people at the time.